Circular knitting machines generally include rotating cylinders and knitting assemblies for forming tubular knitted fabric. Some such machines also include means for feeding sliver to the knitting assembly. The knitting assemblies include an upper and main bed for forming the tubular knitted fabric. The knitted fabric is delivered in a hanging condition from the main bed and rotates with the cylinder. A takedown assembly is often positioned beneath the knitting assembly to pull the knitted fabric from the cylinder and to flatten the tubular fabric. The takedown assembly thereby rotates synchronously with the cylinder to avoid twisting the fabric as it rotates with the cylinder. The takedown assembly generally includes a plurality of rollers wherein the knitted fabric is fed between the driven rollers so as to apply a preset tension to the fabric. Problems occur, however, because the desired tension on the formed fabric from the takedown assembly may vary due to different stitch construction, different types of yarn, variations in stitch lengths performed, etc. If too much tension is applied to the fabric, the fabric may become torn or the knitting needles may be sufficiently stressed wherein breakage occurs. Accurate control of the tension applied to the fabric as it is processed is fundamental to maintaining high fabric quality.
Prior art attempts of adjusting the torque of the rollers responsive to the tension of the fabric include systems utilizing weights and counterweights. The rollers of such units swivel or rock about a pivot to adjust for the tension in the fabric. As a result, the fabric may be taken down unevenly in that one side of the fabric, is pulled faster than the opposite side. In addition, the fabric is not pulled at a constant tension which occasionally results in the fabric getting stretched and/or torn.
In an attempt to overcome these problems, efforts have been made to keep the rollers of the takedown assembly in a level (rather than allowing it to rock back and forth) position. This has been attempted by controlling the speed of the rollers by means of two adjustable pulleys. The pulleys are each adjustably rotatable to adjust the external diameter of the pulley to thereby vary the speed of rotation thereof relative to the other pulley so that the rollers takedown the fabric more evenly. Unfortunately, this has been only moderately successful and has resulted in excessive wear on the pulley belts which requires constant replacement.
It has also been proposed, such as in U.S. Pat. No. 5,537,845 to Lin, to provide a motor, separate from the motor driving the cylinder and knitting assembly, for applying torque to the rollers of the takedown assembly. That patent is directed to a takedown assembly including a take-up roll for receiving the formed fabric in rolled form. As such, the motor for driving the rollers is adjustable relative to the take-up speed of the take-up roller. According to that patent, the motor is not directly responsive to the tension in the fabric as it is being pulled from the cylinder and the knitting assembly. Additionally, a plurality of motors is required.
U.S. Pat. No. 4,879,886 to Okada et al. is directed to a circular knitting machine including a takedown assembly wherein the knitted fabric is received by a take-up roll. The takedown assembly includes three rollers having a constant torque transmission utilizing magnetic clutches. The takedown rollers depend from and are positioned below the cylinder ring gear and the clutch is positioned on respective ends of a roller thereof. The three rollers include one driver roller and two driven rollers. Torque is applied to the driver roller by a complex arrangement of chains, transmission shafts, bevel gears, pulleys, reduction gears, etc., by a pinion associated with the ring gear. Magnetic clutches are associated with the driven roller wherein if excessive load is transferred to the clutch, slippage occurs.
The takedown assembly according to the '886 patent, however, is in combination with a take-up roll for receiving the knitted fabric in rolled form. It would be impractical for knitting high pile fabrics such as formed by sliver knitting, as discussed below. It is an impractical takedown assembly for a circular knitting machine having a tub for receiving the falling formed fabric. This is because the rollers of the '886 patent extend within the housing of the take-up roll, thereby diminishing its filling capacity. Furthermore, the positioning of the rollers farther from the main bed of the cylinder assembly results in a less effective control of the fabric tension. Additionally, the complex structure of the transmission means for driving the driven roller results in a less effective transmission of torque to the takedown assembly driven by the cylinder ring gear, and multiple clutch systems are used, one on each side of the roller assembly.